1. Field of the Invention
The present invention relates to an hygienic, pressure relief, panel unit for use in sanitary applications involving food products or the like. Although the hygienic assembly is especially useful in preventing excessive build up of pressure in food processing equipment such as grinders, dust collectors or similar apparatus, it also has utility in relieving excess pressure in various types of vessels, buildings and enclosed spaces. The pressure relief device is uniquely designed to present a sanitary construction which inhibits the accumulation of food particles and allows thorough cleaning. More particularly, the present invention relates to a pressure relief panel unit including a panel having at least one line of weakness for rupture when the panel is exposed to a predetermined amount of pressure. An imperforate sheet of chemically inert material is disposed over the panel in covering relationship to provide a media tight assembly until rupture and to present a sanitary surface exposed to the interior of the structure.
2. Background of the Prior Art
Pressure relief assemblies, when coupled with the vent of a structure subject to potential pressure buildup, provide assurance that a predetermined amount of pressure will not be exceeded in the interior of the structure. A typical pressure relief assembly includes a metal panel such as stainless steel or other non-rusting metal with lines of weakness defined thereon. These lines of weakness are manufactured to very close tolerances and are designed to separate at a precise predetermined pressure. The lines of weakness may be either score lines or a series of apertures through the panel.
The lines of weakness defined by score lines allow the manufacture of an assembly which is media tight until rupture occurs. Such assemblies, however, are difficult to manufacture for low-pressure applications, as for example under 10 psig. This is attributable to the fact that the thickness of the metal panel is such that when the material is scored to the extent necessary to cause rupture at a low positive pressure, the remaining metal in the scored area must be so thin that it has very little structural strength. Furthermore, it is difficult at best to manufacture a scored panel with predictable low vent pressure characteristics.
In addition, low pressure relief panels as described are usually subjected to varying pressures during use. As a consequence, the constantly varying pressure produces oscillations in the device which causes the effective burst pressure to vary from that initially established rendering the rupture panel unreliable for its intended purpose.
To overcome this problem, typical low-pressure pressure relief assemblies have lines of weakness defined by a series of apertures or slots. The length of the portion of the panel between the slots, commonly called a tab, determines the rupture point of the panel. With this arrangement, the panel itself can be relatively thick for durability and easier machining but yet provide reliable rupture at the desired low pressure.
As those skilled in the art will appreciate, however, the slotted panel must include imperforate material covering the slots to provide an assembly which remains media tight until rupture occurs. The typically preferred sheet material is PTFE or FEP (commonly known as TEFLON). Specifically, this material includes tetrafluoroethylenehexafluoropropylene copolymer (FEP) or polytetrafluoroethylene (TFE or PTFE). PTFE and FEP are preferred because they are relatively chemically inert and because they present a slick "non-stick" surface.
Although a TEFLON sheet has long been used in association with perforated rupture discs to render the unit impervious to flow of media therethrough, a backup device also containing apertures has been required to cause the sheet to remain in conforming relationship to the rupture disc. Without such backup structure presenting in effect a sandwich arrangement, the TEFLON sheet is subject to pressure exertions which weaken the material to a point that it fails prior to the predetermined rupture pressure being exceeded.
In the case of food products, it is not desirable to utilize an internal perforated panel to hold a TEFLON sheet against a rupture disc or panel because the perforations in the retainer panel serve as cavities for entrapment and accumulation of food particles in the apertures of the interior backup panel or plate. These particles can even work their way between the interior panel and the TEFLON sheet thus preventing effective cleaning. This has an adverse effect on the hygienics of the food processing or conveying equipment. It thus is essential that the internal face of the rupture device be sufficiently smooth and cavity free as to substantially avoid entrapment or retention of food particles for any significant period of time.
It has not heretofore been feasible to adhesively affix a TEFLON sheet to a rupture panel or disc because the smooth non-stick surface of the TEFLON prevents reliable bonding of the adhesive thereto. Accordingly, the prior art points out the need for a pressure relief panel unit which presents a sanitary design suitable for food environments.